1. Field of the Invention
The present invention relates to a method for controlling an overload of a main processor of a distributed switching system with a hierarchy structure, and more particularly to a method for controlling a traffic overload occurring in a main processor of a switching system in which processing of subscriber calls and trunk calls are performed in a distributed manner while a number translation, a connection between space switches, and recording of accounting are performed in a centralized manner by main processors.
2. Description of the Prior Art
Conventional methods of controlling an overload of a main processor in a switching system with a hierarchy structure are classified into methods for determining the overload of the main processor and methods for controlling the overload of the main processor. As methods for determining the overload of the main processor, there have been known a method using a CPU occupancy rate, a method using a service queue of processors, and a method using the number of services required in the processors. In the case of the method using the number of services, a determination that the overload of the main processor has occurred is made when the number of services is not less than a particular critical value. As methods for controlling the overload of the main processor, there have been known a method of determining a call service ratio between call services to be accepted and call services to be suppressed in a control interval in accordance with the level of the overload, and a method of determining an interval of accepting all call services and an interval of suppressing all call services.
In the case of determining the overload only using the CPU occupancy rate, a determination that the overload has occurred may be made even if nothing interferes with the call processing service. This is because the CPU occupancy rate may be increased due to an operation maintenance software irrespective of call processing traffic. The erroneous determination results in a degradation in service quality. The present invention complements this method by monitoring a delay of execution of a call processing program and utilizes it for a determination about overload.
In the cases of using the length of the service queue of each processor and the number of calls generated, an analysis of sufficient field operating data and a precisely simulated test are required to derive the critical value used for the determination about overload. Furthermore, these methods have a disadvantage that the derived critical value should be varied depending on the type of call. The disadvantages encountered in the conventional methods of only utilizing the CPU occupancy rate, the service queue and the number of calls generated can be complemented by utilizing both the CPU occupancy rate and the monitoring for the execution delay of the processor.
In the method of controlling the overload, wherein new calls at a next interval are totally suppressed when the CPU occupancy rate is not less than the particular critical value are totally accepted when the CPU occupancy rate is less than the critical value, the control for the overload may be excessive because of an increased width between the increase in service and the decrease in service. On the other hand, the control method wherein the suppression rate is increased as the level of the overload increases has a possibility that an initial control will fail when an overload occurs due to an abrupt increase in load.